1. Field of the Invention
The present invention relates to a push button current cut-off safety switch, and in particular, to a safety switch applying the characteristics of thermal deformation of an alloy to automatically cut-off circuit when it is overloaded, so as to attain the purpose of safety.
2. Description of the Prior Art
FIG. 1 shows an exploded view of a prior art push button switch. When the push button 202 is in the top position of a housing before it is depressed, the contact 206 of a conductive plate 204 and the contact 210 of the connecting leg 208 are separated from each other. When the push button 202 is depressed, the protruded rod 212 of the push button 202 triggers the conductive plate 204 such that the contact 206 contacts with the contact 210.
Thus, the switch is shifted to a conductively connected state. However, this switch provides only the function of ON and OFF, it can not automatically cut off the circuit at a specified current value. As there is no automatic current breaking device in the switch, manual operation is required to shift from ON or OFF state. In order to automatically cut off the current supply to the circuit, there are different kinds of fuse devices available. However, it is not convenient to replace a fuse when it melts. Further, it is necessary to keep a number of fuses in stock for ready use.
In other conventional art, a safety device is employed after the circuit is opened such that by depressing a button thereof, the switch can be restored and ready to use. However, in this prior art, the circuit is very complicated as an additional safety device has to be installed. It is not economical due to greater costs of material, installation and fabrication.
U.S. Pat. No. 5,786,742 relates to a push button switch with an override interruption structure. Referring to FIGS. 1, 2 and 4 to 8 of the patent, the switch comprises a push button 1 connected to contacts 61, 62. When the push button 1 is depressed, the contacts 61, 62 respectively contact with the contacts 731 and 461 of a first conductive plate 73 and a second conductive plate 46 such that the switch is switched to the ON state. This switch employs a well-known mechanism such that when the button 1 is depressed, it remains in the pressed-down position, and the button 1 restores to its original position to open the circuit when the button 1 is depressed once again. In addition, the switch comprises a circuit cut-off device, and when the alloy 75 is overheated, it deforms and causes the push button 1 to be released. Thus the push button 1 restores to its original position, and the contacts are separated. The switch is changed from the ON state to the OFF state.
Accordingly, the present invention relates to a push button current cut-off safety switch, wherein a current cut-off device is mounted within a switch and the shape of the switch is similar to a common switch. In normal operating condition, if the switch is first in a circuit xe2x80x9ccut-offxe2x80x9d state, a depression on the push button changes the xe2x80x9ccut-offxe2x80x9d state into an xe2x80x9cONxe2x80x9d state.
It is another object of the present invention to provide a push button current cut-off safety switch, wherein, the alloy metal is a conducting element within the switch. In accordance with the present invention, if the current via the switch exceeds a specified current value, the alloy metal curves as the temperature increases, and causes an interlinking rod to move. One end of the interlinking rod is in combination with a triangular passage structure such that when an insulating element is pushed to the position between two contacts of the conductive circuit, the circuit becomes a xe2x80x9ccut-offxe2x80x9d circuit. The circuit can be restored to its xe2x80x9celectrically conductivexe2x80x9d state by depressing the push button once more when the alloy metal is cooled without using other tools or changing other elements such as fuse, etc. Thus, the present invention is very convenient to use.
It is yet another object of the present invention to provide a push button current cut-off safety switch, which is reliable while the manufacturing cost is low.
Another object of the present invention is to provide a push button current cut-off safety switch, which is a very safe and convenient device in application.